Electrically operable strikes are well known in the art, and for example, they are used frequently in connection with the main access door of an apartment building to prevent entry into the building until a solenoid associated with the strike is electrically energized to permit pivoting of the strike keeper. See, for example, U.S. Pat. Nos. 4,471,983; 3,638,984 and 3,749,435. Normally, the solenoid is energized by means of a circuit completing switch remote from the strike.
It is also known in the art to prevent release of the latch or keeper of the strike and opening of the door by electrically energizing the solenoid. However, usually there are substantial differences between the components of a strike which will release the keeper with energization of the solenoid and the components of a strike which will lock the keeper with energization of the solenoid.
In addition, the known strikes usually require several components, such as pivotable levers, etc. which increases the assembly problems and the likelihood of malfunctioning because of misalignment, binding or corrosion. Also, if opening force is being applied to the door, the solenoid generally will be unable to cause release of the keeper and/or the components may be unable to prevent opening of the door if a sufficient opening force is applied to the door due to breaking or bending of the locking components.
In general, prior art strikes comprise a single solenoid which has a winding of a conductor which, when electrically energized, actuates an armature which has a locking member connected thereto and biassed by a spring so that the locking member prevents pivoting of the keeper unless the solenoid is electrically energized. To keep the energizing current low, the biassing spring usually has a force which is only slightly more than the force required to return the locking member and the armature to their locking or unlocking positions. Such spring return force may, at times, such as with misalignment of parts, accumulation of foreign matter, etc., be insufficient to return them to their unlocking or locking positions.
It is also known in the art to use an air actuated pistion and cylinder assembly with the piston connected to the locking member to actuate the locking member.